A corticotripin-inhibiting peptide (CIP) has been isolated from human pituitary extracts. It consists of 32 amino acids with a proposed sequence identical to residues 7-38 of adrenocorticotropin (ACTH). The peptide has been synthesized by the solid-phase method. The melanotropic activity of the peptide is estimated to be 30% of the potency of ACTH. It is devoid of corticosteroidogenic activity, but able to inhibit corticosterone production when stimulated by ACTH in isolated rat adrenal cells. Ovine Beta-lipotropin with a linear structure of 91 amino acid residues has been synthesized by the solid-phase method. The synthetic material was purifid by gel filtration, chromatography on carboxymethylcellulose, and partition chromatography on agarose. The final product has been found to be indistinguishable from the natural hormone in its Rf value on partition chromatography, mobility in paper electrophoresis, behavior on thin-layer chromatography, amino acid composition of both acid and enzymic hydrolysates, NH2-terminal residue, behavior on peptide mapping, isoelectric focusing, circular dichroism spectra, optical rotation, lipolytic activity and immunoreactivity. The synthesis of Beta h-endorphin-(1-30) has been accomplished by the solid-phase procedure and its analgesic potency was assayed by the tail fick method. Results showed that the synthetic analog had only 72% activity of the parent molecule. Thus, the complete sequence of 31 amino acid residues in Beta h-EP is required for full analgesic activity.